I. Field of the Invention
This invention relates to connectors for coupling a lead for a tissue stimulating devices, such as a cardiac pacemaker or pacemaker defibrillator, to a pulse generator, and more particularly to a mechanical connector that eliminates the potential for the setscrew becoming locked or stuck in the connector block due to thread damage.
II. Discussion of the Prior Art
Implantable medical tissue stimulators including pacemakers, defibrillators and neural stimulators are used to stimulate tissue such as cardiac tissue or spinal cord tissue with electrical signal. Such tissue stimulators are now quite common and typically comprise a hermetically sealed housing or can containing an electronic circuit and power supply for producing electrical impulses under control of a programmed microprocessor. The pulse generator is connected to target tissue by means of a suitable medical lead. Such leads typically comprise an elongated flexible lead body having a proximal end and a distal end. Disposed at the distal end of the lead are one or more tissue contacting electrodes. The electrodes are connected by wires running through the lead body to associated contacts on a terminal pin at the proximal end of the lead.
The proximal lead terminal pin is adapted to be inserted into a longitudinal bore formed in a header of the stimulating pulse generator. Contained within the header are one or more conductive connector blocks that are connected to feedthrough pins that pass through hermetic seals to join with input and/or output nodes of the electronic circuit contained within the housing. The connector blocks will typically have apertures formed therethrough in alignment with the bore of the header, allowing the proximal lead terminal pin to be inserted through them. To lock the lead in place, the connector blocks will typically include a threaded bore that extends transverse to the longitudinal direction of the bore in the header. Setscrews are inserted into these threaded bores and tightened down against contact areas on the proximal lead terminal. In prior art connector block designs, the last thread convolution or groove gradually reduces in size and terminates within 360 degrees around the circumference. As such, when a setscrew is screwed all the way down when no lead terminal is present in the longitudinal bore of the connector block, the leading thread of the setscrew can extend past the existing threaded area of the connector block. This causes the unmated portion of the leading thread of the setscrew to scrape against a non-threaded area of the connector block. When torque is applied in this situation, the sharp edge on the leading thread of the setscrew will often break off, creating a burr. Furthermore, given the short length of the setscrews employed, and the fact that the final convolution is at an angle to the axis of the setscrew, the resulting angled force on the leading thread can cause the setscrew to tilt within the bore of the connector block. Either of these situations can result in the setscrew becoming lodged in the connector block and the need to scrap the entire pulse generator device—a relatively expensive proposition.
It is accordingly principal object of the present invention to provide an improved connector block/setscrew design that obviates the foregoing problems.